Mirror



Jan. 31,1939. c. A. NICUKLE 2,145,732

MIRROR Filed NOV. 16, 1937' Inventor: Clifford Nickle,-

b4; His Attorney.

Patented J... 31, 1939 UNITED STATES PATENT OFFICE v Y 2,145,732 r I MIRROR New York Application November 16, 1937, Serial No. 174,809

4 Claims.

My invention relates to mirrors and more particularly to mirrors comprising glass provided with reflecting films of vapor deposited metal.

One object of my invention is to provide a pr-oc I 6 ess for stabilizing the deposited metal.

For a better understanding of my invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying draw- 10 ing, and its scope will be pointed out in the appended claims. a

It is now known that metal such as aluminum,

forexample, may be vaporized, preferably in a.

vacuum, and then deposited in-a film, or coating,

on a glass surface to form a mirror surface of chamber, a deposit of metal is obtained in the form of a thin film. This deposit is continued until a substantially light-impervious coating is obtained. It has been found, however, that when mirrors made in this way are required to be cleaned frequently, as in the case where they are used in projectors in which arc lamps are used as the source of light, for example, the frequent cleaning which is necessary removes the metal fllm from the glass.

a In accordance with my invention, this disadvantage is overcome by heat treating the deposited'metal film before the mirror is used. I have found that by heating the deposited layer to a temperature of substantially 150 0., the de- 0 posited particles of metal form a tough continuous or homogeneous coating which will not be injured by the cleaning cloth or other cleaning means ordinarily used for this purpose. The reflectivity of the surface of the coating as a result of this heat treatment also remains substantially constant.

In the; accomp nying drawing, I have illustratedinsectiomamirrorofthetypeusedm projectors. This mirror is'of glass shaped as a paraboloid upon the concave suriaceof which (Cl. ill-49.1)

aluminum is deposited by a known vapor process. In the drawing, I indicates the glass 01' the reflector and 2 indicates the light reflecting film or coating. In accordance with my invention, this form with the deposited film of aluminum 5 thereon is placed in an oven and is heated up to a temperature of 150. The change of state, or rather crystallization, of the vapor deposited aluminum film takes place at a uniform temperature of C. I find, however, that raising 10 the temperature above this value during the treatment insures a uniform product, and I therefore prefer to'raise the temperature of the mir- .ror to after which the mirror is allowed to cool. The actual sintering temperature of 15 aluminum is 250 C. I flnd, however, that heating the mirror to 150 effects a change of state or a crystallization and a toughening of the aluminum film as though it were actually sintered.

The time required for bringing the deposited 2o coatings up to the proper temperature is not critical. The time should, therefore, be regulated in accordance with the requirement of the form upon which the metal coating is deposited.

What I claim as new and desire to secure by 25 Letters Patent of the United States, is:-

1. The process of stabilizing vapor deposited metal reflecting coatings upon vitreous surfaces which comprises heat treating said deposited metal at temperatures substantially below the 30 actual sintering temperature for that metal but not below 110 C.

-2. The process of stabilizing vapor deposited .aluminum reflector coatings upon a glass base which comprises heating said deposited coating 35 cur-moans.moans.- so 

